The invention relates to a torsional vibration damper with at least two structural elements which are rotatable relative to each other against the resistance of at least one energy accumulator and which have biasing areas for compressing the energy accumulator. Furthermore the invention relates to special designs of helical compression springs for use in connection with torsional vibration dampers.
The object of the invention is to provide torsional vibration dampers of the kind described which have a large damping potential and a long service life. Furthermore the object of the present invention is to provide helical compression springs having a particularly high stress potential with a simultaneously high work capacity and/or large energy accumulator capacity. More particularly the helical compression springs according to the invention should be able to be used in cases where the spring windings are strained into a block and are thereby exposed at least at times to high loads. Furthermore the torsional vibration dampers and helical compression springs according to the invention should be capable of a particularly simple economic manufacture.
This is achieved according to one embodiment of the invention in that a helical compression spring serving as an energy accumulator has between its two end windings at least two types of winding with different external diameter, namely a first larger external diameter and a second smaller external diameter, wherein these types of windingsxe2x80x94viewed in the longitudinal direction of the springxe2x80x94are both arranged successively according to a certain pattern and also wound so that the spring has diametrically opposite winding regions which in relation to the longitudinal direction of the helical spring, viewed radially, are located on one side at least approximately at the same height, whilst the diametrically opposite winding regions of the two types of windings are off-set at least approximately by the difference in their external diameters. The stagger can thereby be provided so that when the spring is compressed to a block and before reaching the block length the windings with the smaller and larger external diameters contact one another and are displaced by sliding opposite one another through the purposeful arrangement of the two types of windings relative to each other, so that an additional hysteresis and dissipation of energy is achieved.
It can be advantageous if the two external diameters differ from each other at most by the radial extension of the spring wire in relation to the longitudinal axis of the spring. In many cases it can however also be advisable if this difference in diameter is greater. It can also be advantageous if the two types of windings are arranged at least approximately centrally relative to the centre axis of the spring whereby the external diameters can thereby be matched with each other so that before reaching the block length of the spring the two types of windings contact one another and as already described above produce a friction or friction hysteresis during continued compression of the spring. With a design of the helical compression spring of this kind only the windings with the larger external diameter can where applicable determine the block length of the helical compression spring. The windings with the smaller external diameter are then tensioned between the radially inner areas of two windings of larger external diameter. Through the design according to the invention of a helical compression spring a change in the spring stiffness is possible during compression. This change can be achieved inter alia in that as the two types of windings slide along at least one of these types of windings is elastically deformed in diameter. It is particularly advantageous if the two types of windings are matched with each other so that the windings with the larger diameter are widened at least in some areas whilst the windings with the smaller diameter are compressed at least in some areas in the direction of the longitudinal axis of the spring. The longitudinal axis of the spring is regarded within the scope of the present application as the longitudinal axis which extends through the centre point of the winding with the larger external diameter. In the case of helical compression springs where the two types of windings are off-set relative to each other, the axis running through the theoretical centre point of the windings with the smaller diameter is correspondingly off-set relative to the axis running through the theoretical centre point of the windings with the larger diameter.
According to another embodiment of the invention it is particularly advantageous to use as the energy accumulator a helical compression spring which can be stressed into a block and which has between its two end windings a number of windings of different pitch wherein the greatest winding pitch is furthest away from the end windings. Thus according to the invention there are at least three and preferably more differing winding pitches between the end areas of one helical compression spring. Springs of this kind are preferably made from steel spring wire which can be wound in a so-called hot bending process. Winding can however also take place in the cold state of the steel spring wire or at ambient temperature.
The helical springs according to the invention can be provided in a particularly advantageous way between two relatively rotatable component parts whose rotary movement is restricted by the stop of the spring windings, thus by the springs passing into a block. In a particularly advantageous way the helical springs according to the invention can be installed in the torsional vibration damper of a twin-mass flywheel or a clutch disc or in the damper of a converter lock-up clutch.
Twin mass flywheels are known for example through DE OS 41 17 584 and 37 21 712. Converter dampers are known for example from DE OS 42 13 341. Also the helical compression springs according to the invention can be used in the case of belt dampers as known for example from DE OS 42 25 304 or 42 25 314.
The torsional vibration dampers in which the helical compression springs according to the invention are used are preferably designed so that these are each contained in a segment shaped or ring shaped socket which is formed by the components of the damper elements which are rotatable relative to each other whereby each appropriate socket is formed so that the corresponding helical compression spring is guided both in the radial and in the axial direction therein, namely so that at least when the torsional vibration damper is rotating the spring is supported through the action of centrifugal force on a support surface engaging over same radially on the outside. This support face thereby extends advantageously over practically the entire length of a helical compression spring. Advantageously the helical compression spring is supported directly through its windings on the corresponding support surface. Through the radial support of the helical compression springs through a surface it is possible to produce a friction damping which is dependent on speed or centrifugal force. This friction damping can be produced directly through the spring windings sliding along the corresponding support surface.
The design of the helical compression springs according to the invention can be used more particularly in the case of springs where the length has a multiple of the middle winding diameter. This ratio can lie in the order of between 2.5 and 30, preferably in the order of between 5 and 18.
In the case of helical compression springs which have a number of windings with different pitch between their end windings, it can be particularly advantageous if these springs are designed so that starting from the end windings these each have a spring area whose windings have a pitch which becomes greater as the distance increases away from the corresponding end winding. It can thereby be particularly expedient for many cases if the spring has the largest winding in the centre area and towards the end windings the pitch of the windings decreases at least over a partial area of the spring length which exists up to the corresponding end winding.
It can be particularly advantageous if the windings present between the spring end windings are designed with a different winding pitch so that at least when the spring is blocked the torsional stresses existing in the windings with the larger pitch are greater than the torsional stresses which exist in the windings with the smaller pitch. Thus the material strain in the spring windings can become greater as the winding pitch increases. This material strain can be additionally influenced by corresponding sizing of the middle diameter and external diameter of the windings. Two parameters can thus be used for this, on the one hand the winding pitch and on the other hand the winding diameter.
Advantageously the helical compression springs according to the invention can have a pre-curved shape in the relaxed state. A design of this kind is particularly advantageous in the case of long springs since this makes it easier to fit, thus insert, the springs into the corresponding sockets.
In many cases it can be advantageous if a helical compression spring designed according to the invention is housed inside another helical compression spring or however encloses another helical compression spring. Through such an arrangement an energy accumulator is created which is formed by two helical compression springs boxed axially in each other. With an energy accumulator of this kind at least one of the helical compression springs is provided with windings with a different external diameter and/or with windings of a different pitch.
Furthermore helical springs can be advantageous whichxe2x80x94beginning and ending with a winding of large diameterxe2x80x94have alternate large and small winding diameters, with the centre point axis of the windings with large and small diameters not being the samexe2x80x94namely a concentric arrangement of the windings along their axial extension but the centre point axes of the windings with smaller diameter and larger diameter being off-set radially relative to each other so that on one side of the winding circumference the windings of small diameter can be inserted axially at least in part into the internal circumferences of the windings of larger diameter and on the other side can be mounted at the same radial height. It can be advantageous to arrange the winding circumferences with the insertable windings of small diameter in the direction of the external circumference of a torsional vibration damping device so that the radially outwardly larger compression path of the springs can be compensated for and the spring capacity optimised and the springs can be suspended in the corresponding sockets so that rotation is prevented. Springs of this kind can advantageously be used in numerous other applications, for example in release devices as over dead centre springs, compensation springs and/or return springs and the like.